1. Field of the Invention
The invention relates generally to devices and methods used in the cleaning of tanks and reservoirs on offshore supply vessels in the oilfield industry, and more particularly to those devices and methods which employ a heated fluid.
2. Description of Related Art
The cleaning of mud tanks or reservoirs is an important requirement of the oil and gas industry. Offshore supply vessels (OSV's) are in constant need of having their tanks cleaned and prepared for different cargos that are transported to platforms in the Gulf of Mexico and around the world. Typical cargos include oil, distillate, water, oil-based mud, and water-based mud.
During a typical operation, the OSV will be loaded with drilling fluids, such as oil-based or water-based mud at a dock, and the OSV delivers the cargo to an offshore oil production platform for use in its daily operations. Upon delivery of the cargo, the OSV must then return to the port to re-load cargo and deliver cargo again. This cycle may continue for days or weeks at a time with a quick turnaround at the port as long as the cargo remains the same.
However, if the cargo changes characteristics, e.g. oil-based to water-based mud, the tanks must be cleaned and prepared for the different cargo. This cleaning process starts after vessel is in port. The conventional cleaning method is labor intensive and hazardous, because it involves workers performing these tasks in confined spaces with prolonged exposure time to fumes and chemicals.
Most OSV's have wash down nozzles and scavenging pumps mounted in the tanks designed to rinse the walls with potable water and evacuate the waste (potable water included) out of the tank, and then transfer the bulk waste off the vessel. Once the tank has been rinsed by the vessel equipment, a 4-6 man crew must be hired with pressure washers, SCBA's (Self Contained Breathing Apparatus for the confined space exposure), and all required PPE (Personal Protective Equipment) to allow restricted access into the tanks for final cleaning. The disadvantage of the conventional cleaning process is that the OSV is tied up in port for 4-6 hours per tank. On a vessel with 8 tanks, this equates to approximately 40 hours of down or dock time when the vessel cannot be used in normal operation, along with the added expense of the hired crew and hazard insurance. This lowers the vessel's utilization rate and raises the customer's cost dramatically.